A 46-year-old US woman is believed to have acquired HIV from her female partner in a rare case of female-to-female sexual transmission of the AIDS virus.

A 46-year-old US woman is believed to have acquired HIV from her female partner in a rare case of female-to-female sexual transmission of the AIDS virus.

The US Centers for Disease Control and Prevention said Thursday that laboratory testing confirmed the woman from Texas had a virus "virtually identical to that of her female partner, who was diagnosed previously with HIV and who had stopped receiving antiretroviral treatment in 2010", reported Xinhua.

The woman with the newly acquired infection did not report any other recognized risk factors for HIV infection, such as injection, drug use, tattooing, acupuncture and piercing, the agency said.

She supplemented her income by selling her plasma and first tested negative for HIV after donating plasma in March 2012. The Houston Department of Health reported the case to the CDC in August 2012.

The CDC said the likely source of the patient's new HIV infection was her 43-year-old female sex partner who tested positive for HIV in September 2008.

The couple reported they routinely had unprotected sexual contact during a six-month monogamous relationship, the agency said.

According to the CDC, transmission of HIV between women who have sex with women (WSW) has been reported rarely and is difficult to ascertain because other risk factors almost are present or cannot be ruled out.

"Although rare, HIV transmission between WSW can occur," it said.

"The potential for HIV transmission by female-to-female sexual contact includes unprotected exposure to vaginal or other body fluids and to blood from menstruation, or to exposure to blood from trauma during rough sex."